During warm start processing, JES2 performs some checks on the last written time stamps of the checkpoint data sets it is going to use. These tests try to detect cases where JES2 is reading from the wrong checkpoint data set. Ultimately it is the installations responsibility to ensure that the correct data sets are used to start JES2. However, some common problems are detected by JES2. Normally, the $HASP478 message is not highlighted and is issued for informational purposes only. However, if JES2 detects a potential problem with the last written times of the checkpoint data set(s), then the message is highlighted and followed by the $HASP441 WTOR. When this happens, the installation should verify that the time stamps associated with the data set compared with the time the MAS was last active and would have last written the checkpoint. If not, then reply 'N' to the $HASP441 message to terminate in response to $HASP478.